1.1 GG high idle problem

This is doing my head in

The thing I dont understand is that sometimes it runs at 1000rpm or lower for as long as two days but then it can run for a few weeks with a high idle (sometimes up to 1400rpm)  On the days it idles high it normally gets worse as the engine heats up. I also dont get much idle screw adjustment. The screw is all the way in so I cant make it run slower.

Checks I have done so far:

.Timing
.Tuned
.New carb mount fitted
.Cleaned up earth wire to carb (idled great after that so i thought it was   fixed but then the next day it was runnning fast again)
.Checked the inlet manifold was tight

Im planning on checking the idle solinoid works but..

I just cant figure out why its intermittent. What could cause intermittent idle problems? As I said it can be fine for days and then go high again..not just varying idle speed on one journey..

-Intermittent idle solenoid?
-No water in your petrol is there dude?
-Air leaks around the inlet manifold, spray WD40, or the like around it to check for leaks.
-Atmosphere can have an impact on running (long shot)
-Sticky pre-heater flap?

DubNut said

-Intermittent idle solenoid?
-No water in your petrol is there dude?
-Air leaks around the inlet manifold, spray WD40, or the like around it to check for leaks.
-Atmosphere can have an impact on running (long shot)
-Sticky pre-heater flap?

Going to swap the soleoid from my spare carb over and check the mani again tomorrow.
Theres no way there can be water in the tank.
Cant be the flap as it does the same thing with the airbox off

cheers

Other than the solenoid, I cant think what else could be causing it. Check that the advance/retard mechanism on the dizzy is working correctly, and not jamming up, would be a likely cause. Let me know how You get on bud, could be interesting.
Will.

Air leaks create high idle issues, can be something as daft as a vac hose thats split and closes off when driving, etc. Check all pipes and items in the induction air path for bypassing air past the throttle valve.

Turns out it was a crack in a 2-3 month old carb mount

Ah well, good job you found out dude! A very good example of the fact that new part are not Gospel! Was it a VAG part?

Yeah Im just happy its fixed now. It was an after market one. Im going to try and get a VAG one as the one I have just put on is starting to crack as it was just off a spare carb I bought off ebay. It will do for now as its still air tight

Cheers for the help both of you